Human respiratory syncytial virus (HRSV) is a negative-sense, single stranded, RNA paramyxovirus (K M. Empey, et al., Rev. Anti-Infective Agents, 2010, 50(1 May), 1258-1267). RSV is the leading cause of acute lower respiratory tract infections (ALRI) and affects patients of all ages. The symptoms in adults are usually not severe and are typically analogous to a mild cold. However, in infants and toddlers the virus can cause lower respiratory tract infections including bronchiolitis or pneumonia with many of them requiring hospitalization. Nearly all children have been infected by age 3. There are known high-risk groups that infection with RSV is more likely to progress into the ALRI. Premature infants and/or infants suffering from lung or cardiac disease are at the highest risk to develop ALRI. Additional high-risk groups include the elderly, adults with chronic heart and/or lung disease, stem cell transplant patients and the immunosuppressed.
Currently, there is no vaccine available to prevent HRSV infection. Palivizumab is a monoclonal antibody that is used prophylactically to prevent HRSV infection in high risk infants, e.g. premature infants, and infants with cardiac and/or lung disease. The high cost of palivizumab treatment limits its use for general purposes. Ribavirin has also been used to treat HRSV infections but its effectiveness is limited. There is a major medical need for new and effective HRSV treatments that can be used generally by all population types and ages.
There have been several RSV fusion inhibitors that have been disclosed in the following publications: WO2010/103306, WO2012/068622, WO2013/096681, WO2014/060411, WO2013/186995, WO2013/186334, WO 2013/186332, WO 2012 080451, WO 2012/080450, WO2012/080449, WO 2012/080447, WO 2012/080446, and J. Med. Chem. 2015, 58, 1630-1643. Examples of other N-protein inhibitors for treatment of HRSV have been disclosed in the following publications: WO 2004/026843, J. Med. Chem. 2006, 49, 2311-2319, and J. Med. Chem. 2007, 50, 1685-1692. Examples of L-protein inhibitors for HRSV have been disclosed in the following publications: WO 2011/005842, WO 2005/042530, Antiviral Res. 2005, 65, 125-131, and Bioorg. Med. Chem. Lett. 2013, 23, 6789-6793. Examples of nucleosides/polymerase inhibitors have been disclosed in the following publications: WO 2013/242525 and J. Med. Chem. 2015, 58, 1862-1878.
There is a need for the development of effective treatments for HRSV.